This invention relates to a wireless sensor-network system for transmitting sensor data through wireless communication, and more particularly, to a method of synchronizing sensor data obtained by a plurality of sensing terminal nodes.
In a wireless sensor-network system, environmental data is obtained at multiple points and the obtained environmental data is collected. The environmental data is obtained by measuring temperature, acceleration, pressure, and the like, which represent a state at each of the multiple points. In order that the wireless sensor-network system may correctly process the measured environmental data, a plurality of sensing terminal nodes installed at the multiple points away from one another are required to measure the environmental data simultaneously with one another. In other words, the wireless sensor-network system is required to accurately synchronize the environmental data transmitted from the plurality of sensing terminal nodes installed at the multiple points away from one another.
An example of the method of synchronizing environmental data measured at multiple points includes a method in which each sensing terminal node receives a signal, such as the Global Positioning System (GPS) signal, or a standard time and frequency signal, corrects an internal clock of the sensing terminal node based on the received signal, and adds a time stamp based on a standard time to the measured environmental data (see, for example, JP 2007-018211 A).
Alternatively, there is another method for use in a wireless sensor-network system in which the sensing terminal nodes are connected to one another through wired connection. According to the method, each sensing terminal node periodically obtains a clock value provided to a reference sensing terminal node, and adds the obtained clock value to environmental data (see, for example, JP 2004-187040 A).